Float glass tank with replaceable bottom wall means



March 31, 1970 KlYosHl ITAKURA 3,503,728

FLOAT GLASS TANK WITH REPLACEABLE BOTTOM WALL MEANS Filed Feb. s, 196'? g3g, lL-bm, www

United States Patent O FLOAT GLASS TANK WITH REPLACEABLE BOTTOM WALL MEANS Kiyoshi Itakura, Kobe, Japan, assgnor to Nippon Sheet Glass Co., Ltd., Osaka, Japan Filed Feb. 3, 1967, Ser. No. 613,958

Claims priority, application Japan, Feb. 14, 1966,

41/ 8,401 Int. Cl. C03b 18/00 U.S. Cl. 65--182 8 Claims ABSTRACT OF THE DISCLOSURE Sheet glass manufacturing apparatus contains a molten metal bath and includes a bottom wall floor being made of refractory material and being provided with external cooling means. The bath is partitioned into two or more zones by means of at least one dam traversing widthwise of the bath. The iioor of the bottom wall in at least one of the zones is replaced in part with a member having better thermal conductivity than the other parts of the floor. The result is to achieve transverse temperature uniformity across the width of the molten metal bath.

This invention relates to the control of the temperature of a metal bath, which is used in the method of making glass continuously by utilizing a molten metal bath.

In a method of making sheet glass wherein a molten metal bath is employed, the molten glass is continuously spread out upon said bath into a ribbon, and is cooled as it advances over the bath to be solidified to such an extent that it will be not be damaged when being conveyed by the transporting rolls, following which it is removed from the bath and submitted to the subsequent operations. In forming and cooling the glass ribbon as it proceeds over the molten metal bath, it is necessary for obtaining products of good quality to regulate carefully the changes in the temperature of the bath longitudinally thereof. Heretofore, the necessary changes in the temperature of the bath was accomplished by merely heating the metal bath along its length at differing degrees. A temperature control technique of this sort however requires a very long metal bath and is economically unfavorable. Furthermore, in those instances in which the atmosphere covering the molten metal bath contains even a small amount of an oxidizing component such as CO2, H2O or O2, there is a temperature zone in which turbidity occurs on the undersurface of the glass ribbon. Hence, for obtaining good quality glass the glass ribbon which is being advanced over the bath must be frequently made to pass through this temperature zone at a fast rate. In other words, an abrupt change in the temperature of the bath in certain zones longitudinally thereof is frequently desired. Another problem is the matter of nonuniformity of the temperature widthwise of the molten metal bath. Both side edges of the metal bath tend to become colder than the middle of the bath, with the consequence that the temperature of the middle of the bath is higher than its both edge portions. This nonuniformity of the temperature widthwise of the bath brings about nonuniformity in the thickness of the product widthwise thereof.

This invention provides a sheet glass manufacturing apparatus comprising a bath of molten metal whose function is to receive thereon molten glass fed at a controlled rate, which glass is rendered into a ribbon and advanced over said bath, a basin of said bath being made of refractory material and provided with external cooling means for cooling said basin, characterized in that said molten metal bath is partitioned into at least t-wo zones 3,503,728 Patented Mar. 31, 1970 ICC by means of at least one dam which traverses widthwise of the bath and that at least one part of the oor of at least one of said zones has better thermal conductivity than the other parts of the Hoor.

According to this invention, not only can the length of the molten metal bath be made shorter than those used heretofore, but also the regulation of the temperature such that its uniform distribution widthwise of the bath as well as the desired changes in the temperature longitudinally of the bath can be accomplished very readily.

Referring to the accompanying drawings, FIG. 1 is a schematic side view in longitudinal section illustrating an embodiment of this invention, FIG. 2 being a schematic sectional plan view of FIG. 1; and FIG. 3 is a schematic side view in longitudinal section, as in the case of FIG. 1, illustrating another embodiment of the invention.

In the drawings, the numeral 1 denotes the molten glass, 2, the lip tile, 3, the damper for adjusting the amount of glass iiowing down and 4, the glass ribbon. The numerals 5, 6, 7 and 8 indicate the refractory material which is used for the iioor of the bath, while 9 is the refractory material which constitutes the side walls of the bath. The numeral 10 denotes the dams, 11, the floor coolers, 12, the coolers at the upper part of the side walls, and 13, the burners. Coolers 11 and 12 are of the water-cooled type.

The bath is partitioned into a heating zone 15, an adjusting zone 16, a rapid-cooling zone 17 and a slowcooling zone 18, between which zones dams 10 are provided. Dams 10 serve to hold the commingling of the molten metal to a minimum, and thus temperature control is had over the molten metal in the several zones independently of each other. Tin and the like are used for the molten metal. The material used for the dams 10 is one which not only possesses relatively strong mechanical strength but also which is not corroded by tin nor is easily wetted by the molten glass. For example, graphite and the like are used.

The molten glass 1 which is fed onto the molten metal bath is formed into a sheetlike glass of a given thickness at the heating zone 15 where the temperature of the tin is at about 1000 C., and then it proceeds over the metal bath and is delivered to the adjusting zone 16.

In the adjusting zone 16, the tin temperature in the middle part widthwise of the metal bath, can be lowered by replacement of the floor bricks of the metal bath in said part with an insert-like member of a material, e.g. graphite 19, which is spaced from both lateral side walls, and which not only has better thermal conductivity than the material of the other parts of the ioor but also does not react with the molten tin often used for the bath medium. The metal bath has a tendency wherein the bath widthwise thereof becomes cooled at its two sides with the consequence that the temperature at the middle part becomes higher. However, 'by providing as described hereinabove the tin temperature in the middle of the bath can be lowered to uniformalize the temperature distribution transversely of the bath. Side walls and other parts of the floor of the metal bath, except the part of said Iiioor where graphite is used, are constituted with ordinary refractories whose thermal conductivity is inferior to graphite.

In the rapid-cooling zone 17 a part of the floor bricks of the metal bath is replaced over its entire width with a material 20 such as the aforesaid graphite which has better thermal conductivity than the material of the other parts of said oor, thereby ensuring a drop in the temperature of the tin bath of at least about 20G-400 C. from that of the adjusting zone 16.

The slow-cooling zone 18, on the other hand, has the function of gradually cooling the glass ribbon which has been cooled in the rapid-cooling zone and uniformalizing Y the temperature distribution of the glass ribbon. For this purpose, the middle part 21 of the floor bricks in the lateral direction of the'metal bath is also replaceable with the aforementioned graphite, in a manner similar to that for piece 19 in zone 16, thereby accomplishing the lowering of the temperature of the glass ribbon while uniformly controlling the temperature distribution widthwise of the metal bath.

The temperature of the metal bath is maintained at above l000 C. in the heating zone and ca. 550 C. in the slow-cooling zone. Further, the whole Hoor of the slow-cooling zones does not have to be provided with a cooler; the cooling means may be just provided at the graphite part.

Further, as shown in FIG. 3, instead of replacing a part of the floor bricks of the adjusting zone 16, rapidcooling zone 17 and slow-cooling zone 18 with a material having good thermal conductivity, as hereinbefore described, the refractory material 19, 20 and 21 of FIG. 1, which constitute the essential parts of the oor of the bath, can be replaced with thinner refractory materials 22, 23 and 24, thereby reducing the temperature of the tin which comes in Contact with the thinner refractory material, and thus attaining the same results.

What is claimed is:

1. Tank apparatus for manufacture of flat sheet glass by the lloat process wherein a tank-supported bath of molten metal is utilized to floatingly receive thereon a ribbon of molten glass fed and advanced at a controlled rate over said bath, comprising in combination:

(a) a tank including interjoined bottom, side and end wall means formed of a refractory material different from and having a lower thermal conductivity than graphite and receiving and supporting a molten metal bath therein;

(b) dam means for partitioning said tank and molten metal therein into at least two positive and separate zones by at least one dam member which traverses the tank widthwise,

(c) the bottom wall means of said zones of said tank being disposed substantially co-planar on the interior of the tank throughout the zones length thereof, and said darn means projecting upwardly substantially above the said co-planar level of the interior bottom wall means, but terminating at less than the level of the metal bath used therein to effect the positive separation of said zones,

(d) said bottom wall means of at least one of said zones being replaced in part with a graphite member positioned at a central portion spaced from both lateral side ends of the bottom wall means, whereby the temperature of the molten metal at a position corresponding to said central portion is dissipated through said graphite member to help uniformalize the temperature distribution transversely of the molten metal bath.

2. Tank apparatus as dened in claim 1 wherein the dam means of paragraph (b) include a plurality of spaced transverse dam members to define a first heating zone, an adjusting zone, and rapid-and-slow cooling zones, and said bottom wall means further includes means to vary the thermal conductivity of one transverse portion thereof in each of said zones following the initial first-heating zone and in those zones other than the at least one zone defined in paragraph (d).

3. Tank apparatus for manufacture of flat sheet glass by the float process wherein a tank-supported bath of molten metal is utilized to floatingly receive thereon a ribbon of molten glass-fed and advanced at a controlled rate over said bath, comprising in combination:

(a) a tank including interjoined bottom, side and end wall means formed of a refractory material receiving and supporting a molten metal bath therein,

(b) dam means for partitioning said tank and molten metal therein into at least two positive and separate zones by at least one dam member which traverses the tank widthwise,

(c) the bottom wall means of said zones of said tank being disposed substantially co-planar on the interior of said tank throughout the zones length thereof, and said dam means projecting upwardly substantially above the said co-planar level of the interior bottom wall means, but terminating at less than the level of the metal bath used therein to effect the positive separation of said zones, and

(d) said bottom wall means in at least one of said Zones being replaced in part with an insert-like member of refractory material having a smaller thickness than that of said bottom wall means, said thinner refractory material member being inserted into a central portion of said bottom wall means spaced from both lateral side ends of the bottom wall means, whereby the temperature of the moten metal bath at a position corresponding to said central portion is reduced through said thinner refractory material member to uniformalize the temperature distribution transversely of said bath.

4. Tank apparatus as defined in claim 3 wherein the insert-like member of paragraph (d) is of the same kind of refractory material as that of the other bottom wall means.

v 5. Tank apparatus as dened in claim 3 further including cooling means adjacent said tank walls to selectively expedite dissipation of heat therethrough.

6. Tank apparatus as defined in claim 3 further including cooling means adjacent said tank walls to selectively expedite dissipation of heat therethrough, said cooling means including separate cooling circuit means embracing said side and end wall means to selectively expedite dissipation of heat therethrough.

,7. Tank apparatus as defined in claim 3 further including cooling means adjacent said tank walls to selectively expedite dissipation of heat therethrough, said cooling means including separate cooling circuit means adjacent said bottom wall means to expedite dissipation of heat therethrough.

8. Tank apparatus as defined in claim 3 further including top wall means spaced above the molten bath to enclose the tank, said top wall means including means separating said top wall into zoned segments and heating means in said top wall throughout the respective zoned segments to help maintain the metal bath at a temperature above l000 C. in the initial first heat zone and at progressively lower temperatures to about 550 C. in a last or slow-cooling zone.

References Cited UNITED STATES PATENTS S. LEON BASHORE, Primary Examiner E. R. FREEDMAN, Assistant Examiner U5, Cl- Xflf 65--65, 99, 374 

